In common practice, pigment ink has superior image solidity of printed matter in comparison with dye ink, and is used in inks for wide-format color inkjet recording for commercial signs and displays, and in applications that take advantage of the characteristics thereof. In this color inkjet recording, three-color ink sets comprising pigment inks of the three colors yellow (Y), magenta (M), and cyan (C) (which are the three primary colors of subtractive color mixtures), or four-color ink sets with black (K) added to these are used to render a variety of hues.
However, the above-described three-color or four-color ink sets have drawbacks such as a narrow color reproduction range and reduced color saturation of printed portions (mixed color portions) having secondary and higher color, and have not achieved a level that is capable of providing printed matter with-high image quality comparable to silver-salt photography, process-printing, and the like.
A method of increasing the pigment concentration of each color in YMC ink, a method of increasing the quantity of each color of YMC ink applied to the recording medium, and other methods have also been adopted to solve the problem of reduced color saturation by enhancing it, but all these methods have drawbacks such as a reduced glossy look and the inability to produce the feel of a photograph even when glossy paper is used as a recording medium. Pigment types for YMC inks with ideal spectral characteristics suitable for subtractive color mixtures must be selected in order to effectively spread the color saturation solely with the three primary color (YMC) inks, but the number of pigment types having excellent light fastness, gas resistance, and the like is limited, and when an attempt is made to enhance color saturation among such limited pigment types by increasing the pigment concentration as described above, there is the risk that the hue of the three primary colors may change, the inkjet printer nozzle may clog, or other undesirable effects may occur, resulting in lost efficiency.
A color inkjet ink set for color prints comprising at least one color selected from among orange, green, and violet, each containing a specified pigment, in addition to the three pigment ink colors YMC, is disclosed in Japanese Patent Application Laid-open No. 2000-351928 as a pigment ink set with a wide color reproduction range, but this ink set cannot be said to have an adequately wide reproduction range of color saturation, and is not capable of increasing the color saturation without having an adverse effect on the glossy look. More particularly, it is not capable of raising the color saturation of vermilion without having an adverse effect on graininess. An ink set comprising the two characteristic pigment ink colors orange and green, in addition to the four pigment ink colors YMCK, is disclosed in WO99/05230, but while having excellent reproducibility of colors with high brightness and low color saturation, such as colors with pastel tones, this ink set has an inadequate reproduction range of color saturation with regard to other colors in the same manner as the above-stated ink set, and is not capable of enhancing color saturation without adversely affecting the glossy look.
Thus, conventional pigment ink sets are not capable of providing printed matter with a wide color reproduction range, high color saturation, and high image quality without-adversely affecting the glossy look.
Providing printed matter with superior graininess and high color saturation is particularly desired in relatively small photographs and the like (L size or the like).
Printed matter recorded with an inkjet using a conventional pigment ink set has a drawback which causes so-called metamerism, a phenomenon whereby the hue changes when a different illuminating light source is used. This metamerism is particularly pronounced in composite black- or gray-based hue portions formed with the three color inks YMC, and is a source of reduced image quality.
Consequently, an object of the present invention is to provide a highly reliable ink set as an ink set for inkjet recording capable of providing printed matter having a wide color reproduction range, high color saturation, good graininess, and an adequate glossy look.
Another object of the present invention is to provide an inkjet recording method that uses the above-stated ink set, wherein this inkjet recording method is capable of providing printed matter that has high image quality and reduced metamerism.